The present invention relates to disc filters, and in particular, to the disc filters described in U.S. Pat. No. 5,797,978 and 4,661,250, the disclosures of which are hereby incorporated by reference.
U.S. Pat. No. 5,797,978 discloses a filter which includes a plurality of discs arranged in a stack and having ribbed contacting faces defining small filtering passageways between the contacting faces of adjacent discs, similar to the construction described in U.S. Pat. No. 4,661,250. The filter of U.S. Pat. No. 5,797,978, however, is particularly useful as an air filter. For this purpose, each disc has an embedded electrically- conducting (metallic) electrode layer that is connected to a voltage source to generate an electric field in the spaces between each pair of adjacent discs.
The passageways described in U.S. Pat. No. 4,661,250 and 5,797,978 are created by the geometrical pattern formed on the faces of the discs. The preferred embodiments described in those patents are based on a specific pattern having a continuous rib of a sinuous configuration on one side, and a plurality of annular ribs on the other. For filtration of fine dust particles, the height of the annular ribs must be as small as the particle size, of the order of a few microns. The same applies to the distance between the annular ribs. However because of production limitations, it is difficult to make the ribs of a width, and the spacings between ribs, of such a small size. In practice the opening of each passageway is generally of rectangular shape and of the size in one dimension as needed to block particles, but much larger in the other dimension; i.e., the distance between the annular ribs is greater than their protrusion. Moreover, since the practical thickness of the sinuous rib is about 0.5 mm as dictated from structural considerations, the shape of the passageways is more like a tunnel than like a window. This shape, although exhibiting a low resistance to air flow, restricts further reduction of the resistance to flow because of the production limitations mentioned above.
The metallic electrode layer described in U.S. Pat. No. 5,797,978 is continuous and uniform, so that the electric field generated in the spaces between the discs is homogeneous. Such a homogeneous field is effective to attract charged dust particles. In some cases, however, a portion of the dust particles is uncharged (as a result of humidity for example), whereby the efficiency of the field to attract such dust particles is considerably reduced. A gradient electric field would cause uncharged particles to form electric dipoles which would enhance their attraction by the electrical field. Such electric field gradients would be formed when the field is non-homogeneous.
An object of the present invention is to provide a filter disc of a novel construction having advantages in the above respects.
A particular object of the present invention is to provide a filter disc with a new geometrical pattern which replaces the annular ribs and allows for further decrease of the filter resistance to air flow when used in a multiple-disc filter. Another object of the invention is to provide a filter disc with an electrically-conducting electrode layer which generates a non-homogeneous field among the discs when used in a multiple-disc air filter, thereby enhancing the attraction of particles in the air.
Some of these advantages can be adapted for very fine filtration of liquids as well as air; and therefore an additional object of the present invention is to provide a disc having advantages in the above respects for the filtration of fuel, oil, water and other liquids.
According to one aspect of the present invention, there is provided a multiple disc filter, comprising: a plurality of discs arranged in a stack with a face of each disc in contact with a face of the next adjacent disc in the stack; the contacting faces of the discs including surface formations defining small filtering passageways between the contacting faces of adjacent discs for filtering a fluid passing between the contacting faces; the surface formations including: a rib array of spaced rib sections integrally formed on a flat""surface of one of the contacting faces; and a protrusion array of small, spot-like, discrete protrusions spacing the rib array of the one contacting face from a flat surface of the other contacting face.
According to further features in the described preferred embodiments, the rib sections of the rib array are of equal height and width; and the protrusions of the protrusion array are of substantially smaller height than the height of the ribs, and are of sufficiently small size, and spacing from each other, such that a plurality of the protrusions extend across the width of the rib sections.
In one described embodiment, the rib sections of the rib array are defined by a single rib of sinuous configuration. The discs are of circular configuration, and the spaced sections of the sinuous rib extend radially of the respective disc on which the rib is integrally formed.
Two variations of this embodiment are described. In one variation, the stack includes discs of a first type alternating with discs of a second type; the first type of discs including the rib array on each of its opposite faces; the second type of discs including the protrusion array on each of its opposite faces. In a second variation, the stack includes discs of all the same type, each disc including a rib array on one of its faces, and a protrusion array on the other of its faces.
A further embodiment is described wherein the protrusion array is integrally formed on the outer surface of the rib array of the one contacting face, and is effective to space the rib array from the flat surface formed on the other contacting face. In one variation of this embodiment, the stack includes discs of a first type alternating with discs of a second type; the first type of discs including the rib array and the protrusion array on each of its opposite faces; the second type of discs including flat surfaces on each of its opposite faces. In a second variation of this embodiment, the stack includes discs of all the same type, each disc including a rib array and a protrusion array on one of its faces, and the flat surface on the other of its faces.
The invention is particularly useful in filtration discs including an electrical field formation for removing the solid particles, in which case at least some of the discs are of insulating material and include electrodes mutually-insulated from each other by the insulating material of the discs.
According to another aspect of the present invention, there is provided a multiple disc filter comprising a plurality of discs arranged in a stack with a face of each disc in contact with a face of the next adjacent disc in the stack; the contacting faces of the discs including surface formations defining small filtering passageways between the contacting faces for filtering a air passing between said contacting faces; at least some of the discs being of insulating material and including electrodes mutually-insulated from each other by the insulating material of the discs; alternating electrodes being connected to a first terminal for connection to one side of a voltage source, and the remaining alternating electrodes being connected to a second terminal for connection to the opposite side of the voltage source; each of the electrodes being of planar configuration and being formed with a plurality of closely-spaced gaps bridged by adjacent discs of insulating material and producing gradient electrical fields at the gaps.
The filtration disc may be made without a metallic layer so that no electric field is generated. While this configuration may be limited to filtration of liquids like fuel, oil and water it will be more effective for fine filtration since it provides filtration openings of sizes in the few microns range while the resistance to flow is lower than that in the prior art.
Further features and advantages of the invention will be apparent from the description below.